A4000 DIY Motherboard

[Mathesar]

Originally Posted by elenachen

Well, if they want, they can build their own adapters to the ATX Power slot.....or put a resistive load on the 12V Rail.

Don't want to do some mock up Adapter or a need for a proper Isolated Bench Power Supply......

I can give infos on a howto for loading the 12V Rail while releasing the board.

You could also build in a 12V/5V stepdown converter and only power the board from +12V. Any external brick or simple industrial frame PSU will then do. As far as I can tell -5V is not used anywhere in the system and -12V is only used by the audio circuit. The latter one is quite easily converted into a single-ended version that only needs +12V. I could even do it if you wish

[MigaTech]

Originally Posted by Mathesar

-12V is only used by the audio circuit. The latter one is quite easily converted into a single-ended version that only needs +12V. I could even do it if you wish

On the A1200 if -12v isn't supplied the op amps spit out distorted sound.

[Mathesar]

Originally Posted by MigaTech

On the A1200 if -12v isn't supplied the op amps spit out distorted sound.

But then we just redesign the circuit a bit so that it does work with only +12V. It is really not difficult to do. The first opamp is already biased at about +2.5V. if replaced by a modern rail to rail opamp (we are living in the 21st century after all ) that one and the filter opamp should be just fine. The final opamp could be done away with by moving the gain to one of the first two amps and you're done. The filter enable/disable FEt can be replaced by any modern bidirectional analog switch. Saves a few discrete components.

Like I said, I can draw up and simulate something if desired.

[elenachen]

If you want to mod it to your needs. You can do it after I release it. It'll be open source anyway. But I'll go with ATX Supply, to keep it easy.

[elenachen]

If someone of you is bored. There is a latch needed for the Soft Power on/off of the Power Supply --> It'll be feeded through the +5VSB Line and it needs to pull the PS_ON Line directly to GND.

First press: Pull PS_ON to GND
Second press: disconnect PS_ON from GND --> floating

Would be really nice if someone of you that already has parts lying about could build something up and test it. That would really help.

Thx in advance!

[Daedalus]

Don't forget that the serial circuitry also needs -12V, and that -12V is fed to the Zorro slots so could potentially be required by cards there (-5V as well, but a simple linear regulator will give you that from the -12V rail.

All you need for the ATX supply power on circuit is a debouncer and flip flop circuit. Requiring a latching switch negates the ability to use any old PC case without modification, which is kinda the purpose of this redesign after all. Two logic chips will do it - I'm actually working on something similar in the next while, can give you exact details once I have it running.

[elenachen]

yeah, putting in a 7905 for the -5V rail. Serial Port will be cut down to 9 pin --> no -12V for serial then.

E-ATX are more likely newer cases. Had to buy one myself a few years ago for a dual 1366 board.

[Daedalus]

The -12V is present on the 25-pin serial port, true, but isn't actually required for serial operations and I can't think of any device that might require it. It *is* required for the serial drivers used on the Amiga's output stages, and they're the same for 9 or 25 pin ports. You could of course replace the drivers with modern single-rail devices with their own internal negative rail generation, but you need the -12V supply regardless to meet the Zorro specification so it's also possible to use the same common 1488/1489 drivers the Amiga uses.

When I said "any old", I didn't mean old as in age, I meant any random PC case... Sorry, it's a figure of speech that got lost in translation What I was saying is that a latching and debounce circuit should be included for ATX, because having to modify an ATX case to use a latching switch as suggested above, might be quite a big put-off for people.

[elenachen]

-12V Rail is there in ATX Supply anyway, so I don't worry about that.

Using +5V, +12V and -12V Rails of the supply anyway.

I'm currently working on page 3 of the schematics.

Latch will be included on board of course! But someone has to do the work with the schematic for that. I can do that of course, but it'll take extra time and have no parts at hand for that.

For the User, it should just be a plug and play experience. As long as they have a friend soldering the components to the board for them.

[Daedalus]

This all sounds good I'll give you a hand with the latching circuit in a while, once I can find the time to verify that it works.

[elenachen]

Originally Posted by Daedalus

This all sounds good I'll give you a hand with the latching circuit in a while, once I can find the time to verify that it works.

Thx a lot!

[elenachen]

Ps/2 Keyboard and Mouse support will be added. Mouse port will be usb, but needs a ps/2 compatible mouse. Keyboard port will either be ps/2 or usb

[MigaTech]

@elenachen, The USB mouse port you are planning on adding, I take it would accept the optical gamer mouse that the DE9 to USB Jerry adapter can. Those mice are usually 3200dpi onwards, also would it accept wireless USB mice?

Could you add USB port for K/B control perhaps then wireless control, could be added to this?

[elenachen]

Originally Posted by MigaTech

@elenachen, The USB mouse port you are planning on adding, I take it would accept the optical gamer mouse that the DE9 to USB Jerry adapter can. Those mice are usually 3200dpi onwards, also would it accept wireless USB mice?

Could you add USB port for K/B control perhaps then wireless control, could be added to this?

I'll take existing projects into this --> mmkeyboard and probably mkiv mouse

So whatever they are capable will be included. Like i said, mouse probably needs to be ps/2 capable anyway. Don't know if the mkiv would support such huge dpi modes. As i recall, the amiga should be picky with high dpi. But don't know how the fix was, probably downsampling the dpi in hardware. We'll see about that later after I tested the board. If it doesn't work, then an altered firmware should do the trick.

[MigaTech]

Sorry listed wrong specifications, they are 1600DPI optical USB gamer.

[elenachen]

Like I said, we'll see about that after first prototype is built. Doesn't have high priority right now.

[elenachen]

Added the keyboard support to the schematic today. PS/2 or original A4000 keyboard will be selectable via jumpers on the board.

[Magic]

Originally Posted by elenachen

Added the keyboard support to the schematic today. PS/2 or original A4000 keyboard will be selectable via jumpers on the board.

I think that is a great feature!

[shaf]

I like that idea also since i already have an A4000 Towered System, i could just swap most of the components onto the new board and already have an A4000 Keyboard.

Shaf

[elenachen]

For mouse support I'll probably add the ps2m adapter from aminet. It's open source and is properly tested. So there will be a USB Port for the mouse, but it needs to be PS/2 compatible after all.